There are reasons all the big rigs are diesel. First one is that a diesel will generally go about 1/3 farther on a gallon of fuel than a gas rig will. Second is that being turbo charged, the diesel isn't going to lack for air when you climb mountains. Some folks say maintenance is higher on the diesel, but people will debate you on that. The diesel will last longer if you take care of it, however, and that can translate into higher resale value. Finally, the torque curve of a diesel is much better suited for dragging around heavy loads. This will show up when you test drive one of them.
And yes, I drive a diesel. Actually two, my TV and a diesel Jetta VW. And no, I won't go back to gas. Next vehicle I buy, I'm holding out for a diesel, whether it's a car or a new TV.